(1) Field of the Invention
The present invention relates to a method of fabricating a honeycomb structured panel provided with at least one fastener element, e.g. a floor panel provided with at least one fastener element for fastening equipment of a vehicle. The invention also provides an aircraft panel fabricated by the method.
The invention thus lies in the field of fabricating cellular panels, and more particularly it lies in the field of fitting out vehicle cabins, in particular for flying vehicles such as aircraft, rotorcraft, airplanes, or other similar flying vehicles. More specifically, the present invention relates to fitting out floors for such vehicles, which floors are of laminated and honeycomb structure, and they incorporate fastener elements for fastening equipment of the vehicle, e.g. such as seats.
(2) Description of Related Art
In the field of fitting out vehicle cabins, and more particularly in rotorcraft, it is common practice to fit out the floor using panels that are arranged as a laminated structure. This panel structure comprises a cellular core that is thus implemented as a honeycomb and that is confined inside an enclosure formed using a top outer wall and a bottom outer wall of the panel. The enclosure is thus defined between the bottom and top outer walls that are placed around the honeycomb core so as to protect it and so as to form opposite planes respectively for supporting the panel and for supporting movement inside the vehicle cabin. The top and bottom outer panels may be made of metal or out of composite materials.
Since the floor panel has the potential of supporting cabin equipment, e.g. such as seats or any other appropriate equipment, it is common practice to incorporate fastener elements for such equipment in the floor structure. Such fastener elements are commonly inserts arranged as elongate members for locally receiving a complementary fastener element forming part of the equipment.
Civil certification regulations in force require seat fastener elements to withstand predefined load factors. Each floor panel and each fastener element must therefore be dimensioned so as to withstand such load factors.
In addition, the general techniques used for incorporating fastener elements must lead to only minimal increase in the weight of the floor, while nevertheless guaranteeing that they are incorporated in the floor panel in robust and long-lasting manner, and while also avoiding weakening the panel. Furthermore, fastener elements need to be incorporated so as to comply with safety constraints relating to the ability of the floor to withstand deformation, which constraints are particularly severe for flying vehicles, in particular in the event of a crash.
In a first method, during a first fabrication step, a composite panel which is not fitted with fastener elements is made. Thereafter, the bottom and top outer walls are placed on either side of a honeycomb core, which may be constituted by a metal honeycomb or by a composite honeycomb e.g. of the kind known under the name Nida NOMEX®, with films of adhesive being interposed between each of the outer walls and the core. Under such circumstances, the assembly is polymerized while hot so as to secure the core to the bottom and top outer walls on either side thereof.
During a second fabrication step following the first step, the panel is fitted with fastener elements, such as seat inserts, or inserts for fastening the panel to surrounding structures.
In order to fasten a blind insert the following steps are performed:
routing the bottom outer wall and/or the top outer wall to match the profile of the insert that is to be installed by using a routing jig so as to guarantee interchangeability;
stripping out the core situated between the outer walls so as to provide a space for receiving a fastener element, the stripped-out section of the core having dimensions that are greater than the dimensions of the sections routed in the outer walls;
sucking out the particles that remain in the cavities of the core that open out into said stripped-out space;
arranging a fastener element in said space using a positioning jig to guarantee interchangeability;
preparing a sealant mixture, e.g. based on epoxy resin;
injecting the sealant mixture so as to fill said space between said fastener element and the core; and
causing the sealant mixture to set.
In order to fasten a through insert, the following steps are performed:
drilling one of the outer walls of the panel using a drilling jig to guarantee interchangeability;
stripping out the core situated between the bottom and top outer walls so as to provide a space for receiving a fastener element, the stripped-out section of the core having dimensions greater than the dimensions of the routed section in the outer wall;
sucking out particles that remain in the cavities of the core that open out into said stripped-out space;
preparing a sealant mixture, e.g. based on epoxy resin;
injecting the sealant mixture so as to fill said stripped-out space;
allowing the sealant mixture to set; and
drilling right through the panel via said sealant mixture and then adhesively bonding cups to the top and bottom outer walls.
That first method nevertheless presents the drawback of requiring fabrication to be performed in two steps, namely fabricating the panel and then modifying the panel in order to incorporate fastener elements therein. This gives rise to relatively lengthy fabrication time, and to a wide variety of tooling being used, in particular to ensure that the fastener elements are properly positioned.
It should also be observed that the times required for injecting and setting the sealant product are also relatively lengthy, it also being difficult to distribute the mixture uniformly in the cavities of the cells that open out into the stripped-out space.
Document FR 2 106 075 describes installing a fastener element in a sandwich panel, the fastener element being provided with an outer flange and a tube. The tube is contained in an adhesive sheath, and is inserted in a hole made in the sandwich panel. The fastener element is adhesively bonded to the panel by heating the fastener element to melt the sheath which then bonds to the cells of the panel floor, to the wall of the panel that is in contact with the outer flange, and to the tube of the adhesive element.
The method implemented thus consists in initially fabricating the panel and then in fitting it out. It should also be observed that the flange of the fastener element projects from the panel. Furthermore, it should be observed that the time required for heating the fastener element is difficult to control. Consequently, there is a risk of damaging the surrounding zone of the previously-made panel.
Document JP 11-348157 also lies in the field of the invention.